Having a big stack in a poker tournament is not the solution to your problems, despite the confidence that it (quite naturally) fills you with. When you get a larger stack, your playing style needs to change accordingly and move from being a tight aggressive player to working with more hands and loosening up your game. Then, later in the tournament, your stack is the single best asset you have.
Early On: Looser Calls, Play Aggressive
To keep your lead in a no limit tournament (or, indeed, any tournament,) you have to keep putting more chips in your bankroll. If you’ve established a lead early on in the tournament (and indeed, as you are playing in the middle stages), don’t be afraid to start making make looser calls from the flop, limping in hoping to hit a nut hand. Later in the tournament, you may leave hands like 67 or 78 to the side, but if you can afford to gamble a bit with your chips and be more aggressive, don’t be timid.
A common methodology used by many of the best pros is to use their chip size to force much weaker opponents to push all-in on their stack when they’ve got a good starting hand. Let’s say you’re holding KK or any other hand you’d be willing to raise pre-flop — make them pay to play against you. If you play this wisely and don’t overextend yourself, you can quickly accrue notable amounts of chips without placing yourself in too much risk.
A big hand is a great psychological tool against the vulnerable; going in hard on an average hand can cause others to believe that you’re holding the nuts right off the bat. While it’s not 100% foolproof, it can be used against the more timid players and give you the chance to sweep them out of the pot pre (or immediately post-) flop.
Late In the Tournament: Use Your Stack.
If you’re still in a tournament and ahead of the pack as the blinds begin to escalate into nosebleed territory, that stack can be used by itself to make more chips magically appear in your bankroll in much the same manner described above. Go in and buy the blinds whenever possible. Others call this stealing the blinds, but c’mon, you’re putting money in and getting more money out. Don’t tarnish it.
At a certain point in a tournament, you’ll feel t: the need to almost completely disregard the cards if they’re remotely playable and use your chip stack to wage war on your opposition. Don’t be a bully, but do use your knowledge of the other players (especially late in the game when you’re down to a manageable number of faces to take on) to push those who can be pushed and hold back on those who might be able to surprise you still.